FullCalendar library 5.0 was released on 2020/06/21. Since old major releases do not get security or bug fixes, this module needs to be updated to the version 5.x branch, possibly requiring a 8.x-3.x branch. The current library version is 5.3.2 as of 2020/09/06.
https://github.com/fullcalendar/fullcalendar/blob/master/CHANGELOG.md
https://fullcalendar.io/blog/2020/02/changes-in-the-upcoming-v5
Closed: outdated
2.0
Code
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.
I've volunteered to help clean up the FullCalendar issue queue. As part of that effort I'm closing issues open for unsupported versions of the module as "Closed (outdated)".
If this issue is still relevant for version 3.x of FullCalendar, then feel free to re-open it and update the issue version number.